Des Moines frequently hosts marathons, so check for street closures, especially on holiday weekends.
It’s a very bikable city, so be aware of bike traffic, especially downtown.
I wouldn’t recommend visiting these locations in the winter time as Iowa winters can be frigid. The zoo is open in the winter, but only certain exhibits due to cold weather. Most of the places we went would be ideal in spring/summer/fall.
Buy your zoo tickets online to save a few dollars.